Callin backspacing wizards

I want to know how to convert offset in mm to backspacing in inches....for example, what would the backspacing be on a 22x9.5 with 35mm offset20x8.5 with 15mm offset22x9.5 with 30mm offset

I read that 22x9.5 with 12mm is 5.5 backspacing ...Thanks to all that can help me outDJ JON